1. Field of the Invention
The present invention relates to a vertical gallium-nitride (GaN)-based light emitting diode (LED), and more particularly, to a vertical GaN-based LED in which light emitted to a side surface of the vertical GaN-based LED is reflected toward an emission surface, thereby implementing high brightness.
2. Description of the Related Art
Generally, GaN-based LEDs are grown on a sapphire substrate. The sapphire substrate is rigid and electrically nonconductive and has a low thermal conductivity. Therefore, it is difficult to reduce the size of the GaN-based LED for cost-down or improve the optical power and chip characteristics. Particularly, heat dissipation is very important for the LEDs because a high current should be applied to the GaN-based LEDs so as to increase the optical power of the GaN-based LEDs. To solve these problems, a vertical GaN-based LED has been proposed. In the vertical GaN-based LED, the sapphire substrate is removed using a laser lift-off (hereinafter, referred to as LLO) technology.
A conventional vertical GaN-based LED will be described below with reference to FIG. 1.
FIG. 1 is a sectional view of a conventional vertical GaN-based LED. Referring to FIG. 1, the conventional vertical GaN-based LED includes an negative (n-) electrode 110 formed of Cr/Au, a light-emitting structure in which an n-type GaN layer 120, an active layer 130, and a p-type GaN layer 140 are sequentially formed under the n-electrode 110, and a positive (p-) electrode 150 formed of Cr/Au under the light-emitting structure.
A passivation layer 160 is formed under the bottom and side surfaces of the light-emitting structure, except for a predetermined portion of the p-electrode 150 bonded with an external circuit. The passivation layer 160 is formed of an insulating material such as SiO2. The passivation layer 160 prevents the LED from being electrically shorted with its adjacent device.
A support layer 200 is formed on the outermost surfaces of the passivation layer 160 and the p-electrode 150, and supports the vertical GaN-based LED.
A reference numeral 170 represents a plating seed layer acting as a plating crystal nucleus when the support layer 200 is formed using electrolyte plating or electroless plating. Reference numerals 210 and 220 represent first and second plating layers composing the support layer 200.
The plating seed layer is formed of metal, such as Au, Cu, Ta, and Ni, and surrounds the bottom and side surfaces of the light-emitting structure. Therefore, the plating seed layer absorbs some of light emitted from the light-emitting structure, degrading the entire luminous efficiency. That is, because the plating seed layer formed of metal such as Au, Cu, Ta, and Ti has a low reflectivity, it absorbs light directed to the plating seed layer among the light emitted from the active layer. Consequently, the light extraction efficiency is reduced and the brightness is lowered.